Merge branch 'dt/unpack-compare-entry-optim'

"git checkout $branch" (and other operations that share the same
underlying machinery) has been optimized.

* dt/unpack-compare-entry-optim:
  unpack-trees: fix accidentally quadratic behavior
  do_compare_entry: use already-computed path

Author: gitster

tree-walk.c

@@ -320,6 +320,7 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 	struct tree_desc_x *tx = xcalloc(n, sizeof(*tx));
 	struct strbuf base = STRBUF_INIT;
 	int interesting = 1;
+	char *traverse_path;
 
 	for (i = 0; i < n; i++)
 		tx[i].d = t[i];
@@ -329,7 +330,11 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 		make_traverse_path(base.buf, info->prev, &info->name);
 		base.buf[info->pathlen-1] = '/';
 		strbuf_setlen(&base, info->pathlen);
+		traverse_path = xstrndup(base.buf, info->pathlen);
+	} else {
+		traverse_path = xstrndup(info->name.path, info->pathlen);
 	}
+	info->traverse_path = traverse_path;
 	for (;;) {
 		int trees_used;
 		unsigned long mask, dirmask;
@@ -411,6 +416,8 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
 	for (i = 0; i < n; i++)
 		free_extended_entry(tx + i);
 	free(tx);
+	free(traverse_path);
+	info->traverse_path = NULL;
 	strbuf_release(&base);
 	return error;
 }

tree-walk.h

@@ -59,6 +59,7 @@ enum follow_symlinks_result {
 enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_sha1, const char *name, unsigned char *result, struct strbuf *result_path, unsigned *mode);
 
 struct traverse_info {
+	const char *traverse_path;
 	struct traverse_info *prev;
 	struct name_entry name;
 	int pathlen;

unpack-trees.c

@@ -498,13 +498,14 @@ static int traverse_trees_recursive(int n, unsigned long dirmask,
  * itself - the caller needs to do the final check for the cache
  * entry having more data at the end!
  */
-static int do_compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
+static int do_compare_entry_piecewise(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
 {
 	int len, pathlen, ce_len;
 	const char *ce_name;
 
 	if (info->prev) {
-		int cmp = do_compare_entry(ce, info->prev, &info->name);
+		int cmp = do_compare_entry_piecewise(ce, info->prev,
+						     &info->name);
 		if (cmp)
 			return cmp;
 	}
@@ -522,6 +523,39 @@ static int do_compare_entry(const struct cache_entry *ce, const struct traverse_
 	return df_name_compare(ce_name, ce_len, S_IFREG, n->path, len, n->mode);
 }
 
+static int do_compare_entry(const struct cache_entry *ce,
+			    const struct traverse_info *info,
+			    const struct name_entry *n)
+{
+	int len, pathlen, ce_len;
+	const char *ce_name;
+	int cmp;
+
+	/*
+	 * If we have not precomputed the traverse path, it is quicker
+	 * to avoid doing so.  But if we have precomputed it,
+	 * it is quicker to use the precomputed version.
+	 */
+	if (!info->traverse_path)
+		return do_compare_entry_piecewise(ce, info, n);
+
+	cmp = strncmp(ce->name, info->traverse_path, info->pathlen);
+	if (cmp)
+		return cmp;
+
+	pathlen = info->pathlen;
+	ce_len = ce_namelen(ce);
+
+	if (ce_len < pathlen)
+		return -1;
+
+	ce_len -= pathlen;
+	ce_name = ce->name + pathlen;
+
+	len = tree_entry_len(n);
+	return df_name_compare(ce_name, ce_len, S_IFREG, n->path, len, n->mode);
+}
+
 static int compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
 {
 	int cmp = do_compare_entry(ce, info, n);
@@ -661,8 +695,19 @@ static int find_cache_pos(struct traverse_info *info,
 				++o->cache_bottom;
 			continue;
 		}
-		if (!ce_in_traverse_path(ce, info))
+		if (!ce_in_traverse_path(ce, info)) {
+			/*
+			 * Check if we can skip future cache checks
+			 * (because we're already past all possible
+			 * entries in the traverse path).
+			 */
+			if (info->traverse_path) {
+				if (strncmp(ce->name, info->traverse_path,
+					    info->pathlen) > 0)
+					break;
+			}
 			continue;
+		}
 		ce_name = ce->name + pfxlen;
 		ce_slash = strchr(ce_name, '/');
 		if (ce_slash)